Treatment of cresylic acid



Patented Nov. 23, 1943 TREATMENT OF GBESYLIC ACID Cari N. Andersen.Weiiesiey Hills, Mala, assignor to Lever Brothers Company, Cambridge,Mara, a corporation of Maine Application April as, 1940. eriai no.331,151

Claims. (01. 260-827) aromatic compounds, which group of compounds Ishall refer to as phenols. These compounds are known to react withcaustic in solution to form the corresponding phenolates, and from whichthe phenols can be regenerated by treatment with an acid. The purestform of cresylic acid is composed entirely of the three isomericcresols, and has a boiling range of the order of 190 C. to 205 C., theboiling point of the usual mixture of the isomers being in theneighborhood The commercial forms of cresylic acid generallyencountered, however, also contain lower boiling phenols, such asphenol, and higher boiling phenols, such as the various xylenols,thymol, isopseudocuminol, pseudocuminol, carvacrol, cateformed by thethermal decomposition of higher molecular weight compounds and comprise,for example, the thiophenes, thiocresols, mercaptans, sulfides,disulildes. pyridine. quinoline and other heterocyclic compounds.

The cresylic acid from petroleum sources is contained primarily in"cracked" products and fractions, and the pyrolytic decomposition ofpetroleum in the cracking process similarly explains the presence ofimpurities in the cresylic acid derived from this source.

Coal tar cresylic acid usually contains about 0.05% sulfur, and cresylicacid from petroleum sources contains sulfur in some instances as high as1%. The nitrogen content is generally about the same in the acids fromboth sources, and is of the order of about 0.4%. Coal tar cresylic acidchol, durenol, pentamethyl phenol, etc., in varying amounts, and withwhich are usually associated impurities. This composition of commercialcresylic acid is evidenced by the fact that it has a boiling range of180 C. to 230 0., and in many instances the major portion of theingredients boils above 202 C. Cresylic acid is used as a disinfectantand antiseptic and all of the various phenols therein contribute indifferent degrees to its antiseptic action. However, the cresylic acidscontaining a larger proportion of the higher boiling phenols have asuperior antiseptic action and less toxicity and irritatingcharacteristics. Any

such mixtures of phenols, obtained from either coal tar or petroleumsources may constitute the cresylic acid referred to herein, and may betreated in accordance with my invention.

The cresylic acid of commerce also contains compounds other than thephenols, and these are objectionable constituents of the acid. Thesecompounds generally contain nitrogen and sulfur, and a consideration ofthe processes by which the cresylic acid is manufactured will explainthe presence of these objectionable compounds.

The coal tar from which cresylic acid is derived is known to containalmost an unlimitednumber of compounds, and is obtained by the pyrogenicdecomposition of bituminous coal when subjected to distillation in theabsence of air. The nitrogen and sulfur containing compounds most likelyare is usually high in pyridine derivatives, and petrogum cresylic acidis higher in quinoline derivaves. In the manufacture of cresylic acid bypresent day methods, the desired petroleum or coal tar fractioncontaining the phenols, along with hydrocarbons and other compounds, istreated with an aqueous caustic solution. This converts the phenols intoalkali metal phenolates, which are soluble in the aqueous liquid; theimpurities'are also dissolved in this aqueous portion. The solution isseparated from the hydrocarbons and other insoluble ingredients, forexample by decantation. The separated aqueous solution is then treatedwith an acid, such as carbon dioxide or sulfuric acid, which decomposesthe phenolates and regenerates the phenols. This treatment does notseparate the impurities from the phenols, at least to the desiredextent. Such a mixture constitutes the cresylic acid of commerce.

The impurities in the cresylic acid impart an undesirable odor, which isso unpleasant and foul as to make the acid useless for many purposes,particularly where it is to be used in any composition associated withthe human body or the household. The impurities in the acid also resultin an undesirable color, and the acid of commerce is generallycharacterized by its reddishbrown appearance. A treatment with causticand the subsequent regeneration of the phenols does not result in animprovementin the color and the odor,'inasmuch as the impurities aresoluble in the aqueous caustic. Distillation is generally used, butthisincreases the odor-because heat causes the decomposition of disulfldesinto the more odorous monosulfides. The acid derived from petroleumpresents a particularly dimcult problem of purification, which has notbeen satisfactorily solved. This is evidenced by the fact that no methodis presently known for refining petroleum cresylic acids to such adegree of purity as to render them useable alone or in any compositionsto be used in connection with the human body, or in household use.

While known treatments result in some improvements, they do not do so tosuch a sumcient and critical extent as to achieve the desiredimprovements in color and odor. Particularly is this so in acids frompetroleum sources as available at present, which develop an 'undesirableodor upon heating and develop a color upon standing. The impurities inthe acid apparently undergo, enter into, or cause decompositionreactions.

It is an object of my invention to obtain cresylic acid free fromundesirable impurities and to produce a water-white acid of the highestgrade having a characteristic pure phenol odor suitable forpharmaceutical use and other uses in connection with the human body.

It is a further object 01' my invention to provide a process of treatingcresylic acid which can be practiced in connection with the separationof the acid from the coal tar or petroleum fraction containing the same,as well as in the purification of acids previously separated.

It is an additional object of my' invention to provide a simple andeconomical process which can be carried out readily without detractingin any way from the product or materially enhancing its cost.

In accordance with my invention, I achieve these objects by treating thecresylic acid, either at the time it is regenerated or at any timesubsequently, with chemicals that either precipitate or destroy theimpurities.

My invention is based at least in part upon the discovery that analkaline solution of lead may be used to remove the objectionableimpurities from cresylic acid, at least to such an extent as to renderthe resulting product water-white and free from objectionable odors, andthat this treatment does not deleteriously affect the phenolconstituents of the acid nor interfere with the antiseptic anddisinfectant action of the purified product.

I will describe an illustrative embodiment of my invention as applied tocresylic acid of petroleum origin sincethis is the most difiicult torefine, and has not heretofore been refined on a commercial andeconomical scale for the uses mentioned herein. It is to be understood,however, that my invention is equally applicable to the treatment ofcresylic acid derived from coal tar or from other sources.

Referring more particularly to the illustrative embodiment, about 300parts by weight of cresylic acid of petroleum origin is mixed with acaustic solution of lead, known as sodium plumbite, and the mixturerefluxed for about one-half to several hours, after which it ispermitted to settle.

The alkaline solution above referred to may be obtained by mixing partsof sodium hydroxide and 3 parts of lead oxide or other lead compoundsoluble in an alkaline solution. Water is added thereto in a smallamount which insures the development of sufllcient heat to causecomplete solution of the lead oxide. The amount of the caustic used inmaking the solution is not critical and may vary between 1 and parts.Enough should be employed to place the lead in solution, but an excessis generally desirable. For economical reasons, too large an excess isto be avoided since the excess converts phenols to phenolates which mustbe regenerated. The amount of water may vary and any amount that willdissolve the ingredients may be used. Heat is not necessary and is used,merely to speed the reaction.

After the cresylic acid has reacted with the solution as describedabove, the insoluble compounds formed are removed. This may befacilitatecl by adding water to the cresylic acid mixture which assistsin the separation of the insoluble compounds. The alkali is removed bywashing, and sufiicient acid, such as sulfuric or carbon dioxide, isadded to neutralize the sodium phenolates formed during the treatmentwith the alkaline solution and to regenerate the corresponding phenols.The mixture may be washed to remove the excess sulfuric acid. In thepreferred embodiment the material is heated to about 70 C. as this tendsto break down and precipitate any insoluble compounds remaining insolution, and also has the advantage of preventing bumping" duringdistillation.

It may be desirable at this stage to assure the removal of all basicconstituents, and if so the cresylic acid may be thoroughly mixed with asmall amount to 1%) of a mineral acid and then heated to C. The mixtureis then washed with water to remove any excess acid. The dried cresylicacid is ready for distillation which may be either in vacuum or withsteam under reduced pressure. The resulting cresylic acid is waterwhite,and is devoid of the smoky or gassy odor associated with unpurifiedcresylic acid.

It will be apparent that the exact procedure, that is, the relativelength of time of heating, the relative amounts of the ingredients andthe neutralizing and washing operation may be varied depending upon thenature of the cresylic acid to be treated and the amounts and types ofimpurities therein; these factors may be varied over wide limits. Anyalkaline solution of a lead, zinc or other metallic compound of theclass described may be used in a manner similar to that described. Theseveral acid treating and washing steps may be omitted, if the yield isnot important or if a product of the desired purity for the particularuse desired can be obtained without them.

It has been observed that upon the distillation of cresylic acid thathas not been purified to the requisite extent, the distilled cresylicacid is sometimes not as sweet or clean as it was prior to distillation.This is no doubt due to the fact that certain pyrogenic decompositionproducts are formed from the sulfur compounds during the distillationand these impart the undesirable odor to the finished product. Such aproduct is generally referred to as "gassy.

It may be desirable, therefore, in instances where the cresylic acidcontains certain types of impurities, or in excess amounts, to distillthe acid prior to the plumbite treatment in order to decompose suchproducts and render them more readily removable during the plumbitetreatment.

My invention as described above may b utilized in the treatment ofcresylic acid at any stage in its manufacture, in which event theextraction of the acids from any other ingredients associated with thesame is accomplished by means of an alkaline solution of one of theherein mentioned metals as described. If desired.

, move all trace of acid and distilled either in vacuum or with steam atreduced pressure. The resulting product is water-white and of excellentodor.

It will be apparent that my process is capable of any minor alterationsand adaptations as to the exactnature and sequence of the variousoperations described, and I intend all such variations and adaptationsto be included within my invention.

I claim: 1. In a process of treating impure cresylic acid,

5. In a process of purifying cresylic acid having an undesirable colorand odor, the step which comprises heating said acid in admixture with acaustic soda aqueous solution oi sodium plumbite and removing theimpurities rendered insoluble thereby. g

8. In a process of purifying cresylic acid having an undesirable colorand odor, the steps which comprise distilling said acid to decompose atleast some of the impurities, heating said acid in admixture with acaustic aqueous solution of an alkali metal plumbite, and removing theimpurities rendered insoluble thereby.

the step which comprises treating the mixture with an alkaline aqueoussolution of an alkaline soluble lead compound to remove impurities fromsaid cresylic acid.

2. In a process of treating impure cresylic acid,'the steps whichcomprise heating the mixture with a caustic soda aqueous solution ofsodium plumbite, removing the separated undesirable compounds,acidifying the resulting mixture, removing the excess acid, anddistilling the purified mixture.

3. In a process of treating impure cresylic acid to obtain a purifiedcresylic acid, the steps which comprise scrubbing the mixture with acaustic aqueous solution of an alkali metal plumbite, separating thesolution from the residue, acidifying the solution to regenerate anyphenols converted into phenolates by said caustie, and distilling theresulting mixture under reduced pressure.

4. In a process of treating impure cresylic acid to obtain a purifiedcresylic acid, thesteps which comprise scrubbing the mixture with acaustic soda aqueous solution of sodium plumbite, acidifying thesolution to regenerate any phenols converted into phenolates by saidcaustic, removing any acid remaining in the resulting mixture, anddistilling the purified cresylic acid.

7. ma process 01' purifying cresylic acid having an undesirable colorand odor, the step which comprises treating said cresylic acidwith analkaline aqueous solution of an alkali metal plumbite, adding water tothe mixture and removing the impurities, acidifying-the mixture toregenerate any phenols converted into phenolates by said alkali, washingthe resulting mixture to remove acid, and distilling the mixture.

8. In a process of purifying cresylic acid having an undesirable colorand odor, the step which comprises heating said cryslic acid withcaustic aqueous solution of an alkali metal plumbite, adding water tothe mixture and removing the impurities, acidifying the mixture toregenerate any phenols converted into phenolates by said caustic,heating the mixture to further precipitate the insoluble compounds,treating the resulting mixture with an acid, washing the mixture toremove the acid, and distilling the mixture under reduced pressure.

9. In a process of treating impure cresylic acid, the steps whichcomprise treating the mixture with an alkaline solution of an alkalinesoluble lead compound to precipitate impurities from said cresylic acid,separating the undesirable precipitated compounds, and acidifying theresulting mixture to regenerate phenols from any phenolates formed bythe treatment with the alkaline solution.

10. In a process of treating impure cresylic acid, the steps whichcomprise treating the mixture with an alkaline solution of an alkalinesoluble lead compound to separate impurities from said cresylic acid,removing the separated undesirable compounds, acidifying the resultingmixture, removing the excess acid, and distilling the Purified product.

' CARL N. ANDERSB.

